Smoke-like material without simulation?
To elaborate on Joel's recommendation of using smoke sprites: I believe he is suggesting an instanced set of small face primitives positioned in a scattering at the surface of the water object. Vary the transparency, size, and the magnitude of a small animated shimmer movement so that each small face (sprite) has an additive motion overlaid onto the base water object(s) in the waterfall. Also assign material and texture from a collection of smoke pngs.

A key consideration is that these sprite elements should remain roughly normal to the camera view plane...not parallel to the water or its not really acting as a sprite just another texture-mapped animated object.

The cumulative effect of the instancing is to allow variability of the image, shimmer motion, size, position, and transparency while reducing discrete object definitions. The art is in making the sum of sprite variations appear like hydraulic effects such as turbulence!

(Note :if my 'comment all' creds came thru I would have simply commented on Joel's comment instead of adding a new 'answer' with these details.)